1. Field of the Invention
The present invention relates generally to visual display devices. More particularly, the present invention relates to a computer visual display monitor having an integral stereo sound reproduction facility and an integral microphone.
2. Art Background
Video displays are pervasively used as visual output devices for all types of computer systems. Most commonly, a cathode ray tube (CRT) is enclosed within a supporting enclosure together with associated subsystems such as CRT control circuits and power supplies to form a computer visual display unit commonly known as a monitor. The monitor is then coupled to receive video signals from a main processor unit including video control logic.
Prior art monitors have not heretofore incorporated high quality audio capability. In fact, prior art computer systems as a whole have only included minimal, low quality sound generation capabilities for limited purposes such as generating user prompt signals, system warning signals, and others. For example, most personal computer systems incorporate a small relatively low performance speaker to produce the above prompt and warning signals, usually comprising one or more low fidelity "beep" tones, or very simple synthesized speech phrases. In low performance audio applications, construction and placement of the speaker system usually is immaterial. In fact, in most personal computer systems the speaker is typically mounted to a bottom-, side-, or rear-facing panel of the computer endosure, thus leaving the front panel of the enclosure free for user access to mass storage devices contained therein, or other user controls. Remote speaker placement is usually adequate for the above-mentioned prompt and warning signals because such sounds generated by computer systems typically comprise relatively narrow bands of sound without any significant low frequency (bass) components, and are played at low volume levels. When complex sounds such as voice and music are generated or played back through a low quality, arbitrarily positioned speaker, the resulting uneven frequency response severely restricts the utility of the sound system, which is otherwise adequate for simple warning tones.
More recently, with the advent of digital sound recording and processing techniques, the increased use of sound by computers within computing applications, as well as the need for high quality recording and reproduction of sound within personal computing systems, is desirable. However, despite substantial improvements in personal computing system performance in terms of numeric processing speed and visual display clarity, the recording and reproduction of high quality sound within computer systems have not enjoyed similar advancements. In other words, although modern digital recording techniques produce very high quality source material, the recreation of high quality sound from such recorded media within computing environments generally, and personal computing environments specifically, has been extremely poor in the prior art. The foregoing is principally due to the inability to generate high quality full frequency sound from a small panel-mounted speaker, as previously described in connection with personal computer systems. The audio reproduction problem is compounded even further when reproduction of high quality stereophonic sound is desired.
Although relatively high quality full frequency stereophonic sound has been integrated into television environments, such integration is fundamentally different from the application of high quality sound to computer visual display monitors. First, television images are generated by relatively low resolution analog signals, which images can be created on large dot pitch CRTs, i.e., where the illuminating phosphor dots are spaced further apart. By contrast, computer generated images, whether animated or sampled video signals, are significantly higher resolution digital images requiring much finer dot pitch CRTs. Typically, television CRTs employ what is known as a shadowmask to help direct the phosphor-exciting electrons to the appropriate phosphors. Shadowmasks are opaque sheets having as many holes as there are phosphors, which holes are usually grouped in threes with space provided between the groups. Although completely adequate for most television viewing, shadowmasks are inherently performance limited: the hole spacing limits the ultimate resolution, and the mask itself blocks a significant percentage of total electron flux, thereby limiting the CRT's brightness. A few CRTs employ an alternative screening device known as an aperture grill, such as the Trinitron.RTM. CRT manufactured by Sony Corporation. Trinitron.RTM. CRTs employing aperture grills can be constructed in normal resolution as well as high resolution variants, and consist essentially of an arrangement of finely spaced wires which can be caused to vibrate at some resonant frequency. Unlike the larger, normal resolution aperture grills which resonate at a very low frequency or not all, the smaller, high resolution aperture grills used in computer display monitors can have their resonant frequencies well within musical and ordinary listening frequencies. Accordingly, if a high quality stereophonic sound system is brought into sonic communication with a high resolution aperture grill having its natural frequency within the musical spectrum, the grill will vibrate and severely degrade visual image quality displayed on the CRT, usually manifesting itself as shimmering waves of darkness and brightness similar to Moire interference. The foregoing image degradation usually is not encountered in lower resolution displays intended for television use for several reasons, including the fact that television images typically comprise non-static, non-uniform backgrounds. In contrast to typical television images, computer system images frequently include stationary, homogeneous shapes and colors, against which the image degradation due to aperture grill vibration is easily and noticeably seen. However, the aperture grill problem will have to be addressed when designing high resolution CRT display devices incorporating high quality sound reproduction systems, whether for computer environments or for the anticipated High Definition Television (HDTV) systems presently under design.
Finally, prior art computer systems are generally not constructed to facilitate recording of voice signals, in particular for purposes of speech recognition. Where facility for voice recording is provided in prior art systems, typically an external microphone must be maintained in close proximity to the speaker's mouth, for example by gooseneck extension or by a headset arrangement. Such microphone attachment effectively ties the user to the computer and restricts the user's movement. Alternatively in the prior art a microphone may be attached to an exterior surface of a computer system component such as the processor enclosure or the monitor. However, such external attachments typically result in non-optimal microphone performance, where directional characteristics of the microphone, if any are provided by its design, are arbitrarily modified by nearby reflecting surfaces and refracting edges. The result is that the ratio of the desired speech signal to undesired room noise and reflections is unacceptably degraded.
As will be described in the following detailed description, the present invention overcomes many of the limitations associated with prior art computer systems and visual displays by providing an integrated, high resolution, video display monitor incorporating high quality stereophonic sound generation facility as well as speech recognition differential microphone. A user of the present invention can use the integrated monitor of the present invention to display high quality graphics or video data accompanied by full frequency stereophonic sound without compromising the quality of the projected image. Furthermore, the integral directional microphone is positioned and optimized to receive and resolve human speech generated by the computer user, and to provide maximum cancellation of unwanted sounds. The signal from the microphone may then be used for many applications where clear pickup of speech is required, such as voice recognition, teleconferencing, and voice annotation.